Add 'musttail' marker to call instructions

This is similar to the 'tail' marker, except that it guarantees that
tail call optimization will occur.  It also comes with convervative IR
verification rules that ensure that tail call optimization is possible.

Reviewers: nicholas

Differential Revision: http://llvm-reviews.chandlerc.com/D3240

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207143 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 19 insertions, 7 deletions

diff --git a/lib/AsmParser/LLLexer.cpp b/lib/AsmParser/LLLexer.cpp
index 0e75b4612b..c1ba37db0f 100644
--- a/lib/AsmParser/LLLexer.cpp
+++ b/lib/AsmParser/LLLexer.cpp
@@ -512,6 +512,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(null);
   KEYWORD(to);
   KEYWORD(tail);
+  KEYWORD(musttail);
   KEYWORD(target);
   KEYWORD(triple);
   KEYWORD(unwind);
diff --git a/lib/AsmParser/LLParser.cpp b/lib/AsmParser/LLParser.cpp
index 7e11aecd92..56422393e4 100644
--- a/lib/AsmParser/LLParser.cpp
+++ b/lib/AsmParser/LLParser.cpp
@@ -3367,8 +3367,10 @@ int LLParser::ParseInstruction(Instruction *&Inst, BasicBlock *BB,
   case lltok::kw_shufflevector:  return ParseShuffleVector(Inst, PFS);
   case lltok::kw_phi:            return ParsePHI(Inst, PFS);
   case lltok::kw_landingpad:     return ParseLandingPad(Inst, PFS);
-  case lltok::kw_call:           return ParseCall(Inst, PFS, false);
-  case lltok::kw_tail:           return ParseCall(Inst, PFS, true);
+  // Call.
+  case lltok::kw_call:     return ParseCall(Inst, PFS, CallInst::TCK_None);
+  case lltok::kw_tail:     return ParseCall(Inst, PFS, CallInst::TCK_Tail);
+  case lltok::kw_musttail: return ParseCall(Inst, PFS, CallInst::TCK_MustTail);
   // Memory.
   case lltok::kw_alloca:         return ParseAlloc(Inst, PFS);
   case lltok::kw_load:           return ParseLoad(Inst, PFS);
@@ -3984,10 +3986,14 @@ bool LLParser::ParseLandingPad(Instruction *&Inst, PerFunctionState &PFS) {
 }
 
 /// ParseCall
-///   ::= 'tail'? 'call' OptionalCallingConv OptionalAttrs Type Value
+///   ::= 'call' OptionalCallingConv OptionalAttrs Type Value
+///       ParameterList OptionalAttrs
+///   ::= 'tail' 'call' OptionalCallingConv OptionalAttrs Type Value
+///       ParameterList OptionalAttrs
+///   ::= 'musttail' 'call' OptionalCallingConv OptionalAttrs Type Value
 ///       ParameterList OptionalAttrs
 bool LLParser::ParseCall(Instruction *&Inst, PerFunctionState &PFS,
-                         bool isTail) {
+                         CallInst::TailCallKind TCK) {
   AttrBuilder RetAttrs, FnAttrs;
   std::vector<unsigned> FwdRefAttrGrps;
   LocTy BuiltinLoc;
@@ -3998,7 +4004,8 @@ bool LLParser::ParseCall(Instruction *&Inst, PerFunctionState &PFS,
   SmallVector<ParamInfo, 16> ArgList;
   LocTy CallLoc = Lex.getLoc();
 
-  if ((isTail && ParseToken(lltok::kw_call, "expected 'tail call'")) ||
+  if ((TCK != CallInst::TCK_None &&
+       ParseToken(lltok::kw_call, "expected 'tail call'")) ||
       ParseOptionalCallingConv(CC) ||
       ParseOptionalReturnAttrs(RetAttrs) ||
       ParseType(RetType, RetTypeLoc, true /*void allowed*/) ||
@@ -4074,7 +4081,7 @@ bool LLParser::ParseCall(Instruction *&Inst, PerFunctionState &PFS,
   AttributeSet PAL = AttributeSet::get(Context, Attrs);
 
   CallInst *CI = CallInst::Create(Callee, Args);
-  CI->setTailCall(isTail);
+  CI->setTailCallKind(TCK);
   CI->setCallingConv(CC);
   CI->setAttributes(PAL);
   ForwardRefAttrGroups[CI] = FwdRefAttrGrps;
diff --git a/lib/AsmParser/LLParser.h b/lib/AsmParser/LLParser.h
index f5c8a5a26d..e2bf46290b 100644
--- a/lib/AsmParser/LLParser.h
+++ b/lib/AsmParser/LLParser.h
@@ -372,6 +372,8 @@ namespace llvm {
     bool ParseFunctionBody(Function &Fn);
     bool ParseBasicBlock(PerFunctionState &PFS);
 
+    enum TailCallType { TCT_None, TCT_Tail, TCT_MustTail };
+
     // Instruction Parsing.  Each instruction parsing routine can return with a
     // normal result, an error result, or return having eaten an extra comma.
     enum InstResult { InstNormal = 0, InstError = 1, InstExtraComma = 2 };
@@ -398,7 +400,8 @@ namespace llvm {
     bool ParseShuffleVector(Instruction *&I, PerFunctionState &PFS);
     int ParsePHI(Instruction *&I, PerFunctionState &PFS);
     bool ParseLandingPad(Instruction *&I, PerFunctionState &PFS);
-    bool ParseCall(Instruction *&I, PerFunctionState &PFS, bool isTail);
+    bool ParseCall(Instruction *&I, PerFunctionState &PFS,
+                   CallInst::TailCallKind IsTail);
     int ParseAlloc(Instruction *&I, PerFunctionState &PFS);
     int ParseLoad(Instruction *&I, PerFunctionState &PFS);
     int ParseStore(Instruction *&I, PerFunctionState &PFS);
diff --git a/lib/AsmParser/LLToken.h b/lib/AsmParser/LLToken.h
index 00f7fe8c12..ab5a1a535d 100644
--- a/lib/AsmParser/LLToken.h
+++ b/lib/AsmParser/LLToken.h
@@ -54,6 +54,7 @@ namespace lltok {
     kw_undef, kw_null,
     kw_to,
     kw_tail,
+    kw_musttail,
     kw_target,
     kw_triple,
     kw_unwind,